Yes, the 7D is all auto everything when it comes to audio... and even if you could control the gain it would NOT be an option for proper audio recording. It is just not built for Pro Audio. You really need to invest in a separate audio recorder (like a Sound Devices 702 recorder if you are serious... or if on a budget a Zoom H4n) and sync in Post. Right now you can use Plural Eyes ($99) to sync but it looks like FCPX will have this capability built into it when it when it is released next month.